Method of improving production of petroleum from an underground reservoir



June II, 1963 D. L. HOYT 3,093,190

METHOD OF IMPROVING PRODUCTION OF PETRQLEUM FROM AN UNDERGROUNDRESERVOIR Filed April 11, 1960 s Sheets-Sheet 1 Q H NED NDD June 11,1963 D. HOYT 3,093,190

METHOD OF IMPROVING PRODUCTION OF PETROLEUM FROM AN UNDERGROUNDRESERVOIR Filed April 11, 1960 3 Sheets-Sheet 2 I l I 7 x5;

30 Number oF Wells N Tzcyi June 11, 1963 HOYT 3,093,190

METHOD OF IMPROVING PRODUCTION OF PETROLEUM FROM AN UNDERGROUNDRESERVOIR 3 Sheets-Sheet 3 Filed April 11, 1960 flofiez d3 pen J T/I/fi/fi? 25 5 90 '2 /o I4 @Kcm 80 I5 I 9' t 60 I 1 i I3 3, 50 r3 8 I a}I 1 1 9! 30 I 1 I I 20 I I JI I I0 I I 0 5 IO as Number 0/ /IX/ 0/ he/ls -/V United States Patent Ofilice 3,093,190 Patented June 11, 19633,093,190 METHOD OF ROVENG PRODUCTHUN F PETROLEUM FROM AN UNDERGROUNDRESERVOIR Donald L. Hoyt, Houston, Tex., assignor to Texaco Inc, NewYork, N.Y., a corporation of Delaware Filed Apr. 11, 1960, Ser. No.21,485 Claims. (Cl. 166-9) This invention relates generally to therecovery of petro leum from underground reservoirs. More particularly,this invention relates to a method for improving the recovery ofpetroleum from an underground petroleumproclucing reservoir. In aspecific embodiment, this invention is directed to the production ofpetroleum from an underground petroleum-producing formation which isunder the influence of an adjacent, e.g. underlying, waterproducingformation or aquifer.

In the production of petroleum from underground formations, it has beenthe practice heretofore to penetrate the petroleum-producing formationwith a plurality of Wells arranged in a grid pattern, the petroleumbeing produced from the formation via these Wells. It has been observedparticularly when the petroleum-producing formation is a so-called waterdrive formation, i.e. under the influence of a water-producing formationwhich tends to displace the petroleum from the petroleum-producingformation via the production wells, that the wells around the peripheryof the producing formation relatively quickly produce an excessiveamount of water and must be abandoned before substantially all of thepetroleum in that zone of the formation under the influence of theseperipheral wells has been produced.

Accordingly, it is an object of this invention to provide a method forimproving the production or recovery of petroleum from an undergroundpetroleum-producing formation.

Another object of this invention is to provide an improved method forthe production and recovery of petroleum from an elongated,substantially elliptical, petroleum-producing formation which is underthe influence of an adjacent water-producing formation.

Another object of this invention is to provide a method for increasingthe amount of oil which is recovered from an underground, water drive,petroleum-producing formation.

Still another object of this invention is to provide an improved methodfor producing a water drive petroleumproducing formation during primarydepletion as well as during secondary recovery operations.

How these and other objects of this invention are accomplished willbecome apparent from the following description when read in conjunctionwith the accompanying drawings wherein FIGS. 1, 2, 3 and 4 schematicallyillustrate the distribution of petroleum-producing wells producing anelongated petroleum-producing formation.

FIGS. 5 and 6 are graphical showings of results achieved respectively byconventional practice and by practice of this invention.

In accordance with this invention, it has been discovered that theproduction of petroleum from an underground petroleum-producingformation is improved by disposing the production wells producing theformation substantially in line along the length of the producingformation.

plurality of tion Wells. Of these production wells, 12 or 35 percentMore particularly, it has been discovered that the petroleum productionfrom an underground, elongated, substantially elliptical,petroleum-producing formation, which is under the influence of a waterdrive, is improved by disposing the production wells penetrating theformation substantially in line along the major axis of the formation.

Still more particularly, in accordance with this invention, it has beendiscovered that the production of petroleum from an underground,elongated, substantially elliptical, water drive petroleum-producingformation is improved by disposing the production Wells producing theformation so that as many of the production wells as practicable aredisposed substantially in line along (i.e. on or near) the major axis ofthe formation.

As indicated hereinbefore, the practice of this invention is applicableparticularly to improving the recovery of petroleum from elongated,substantially elliptical, water drive petroleum-producing formations.More particularly, improved results are obtained in accordance with thepractice of this invention when the elongated, substantially elliptical,petroleum-producing formation has a major axis at least four timesgreater than the minor axis, e.g. a ratio of major axis to minor axis inthe range of about 4.5-10.0 to 1.0.

Referring now to the accompanying drawings, particularly to FIG. 1thereof, there is illustrated schematically therein an elongated,substantially elliptical water drive petroleum-producing formationwherein the major axis thereof has a length about 4.5 times greater thanthe minor axis. The periphery of this reservoir is delineated by ellipse10. Penetrating the elliptical reservoir 10 is a production wells P, fora total of 34 producor" the total number are disposed in line along themajor axis of the formation and equidistant from each other. Theremaining production wells, P, 22 in number, are disposed, as indicated,in a grid-like pattern with respect to the aforementioned productionwells disposed in line along the major axis of the formation. Laboratorytests on a model simulating the above-described elliptical reservoirindicated that when all the wells are produced simultaneously, there isultimately swept about 86.4 percent of the oil in place in thereservoir, i.e. during production of this reservoir via the 34production wells, 86.4 percent of the reservoir formation was swept bythe displacing fluid (water).

On the other hand, tests conducted on the same reservoir having a totalof 46 production wells, 12 or 26 percent of which are disposed in linealong the major axis thereof, as illustrated in accompanying FIG. 2,indicated that only 86.4 percent of the reservoir was swept. Uponcomparison of the results obtained with the petroleum productiontechniques as disclosed in FIGS. 1 and 2, it is seen that the 12additional wells employed in connection with FIG. 2 did not contributeto any additional production of petroleum from the reservoir andrepresented, in fact, a substantially needless expenditure.

FIG. 3 represents the same reservoir again having a total of 46production wells, but this time 16 or about 35 percent of which aredisposed substantially in line along the major axis thereof. Testscarried out in connection with the production wells disposed in themanner illustrated in FIG. 3 indicated that 90.7 percent of thepetroleum-producing formation would have been swept, with resultingincrease in the production of petroleum. Further, since the total numberof wells has been increased, it is possible to deplete the reservoir ina much shorter period of time along with the substantial increase inpetroleum production.

Finally, the same water drive petroleum-producing for mation was againsimulated and this time all the production wells, a total of 12 innumber, were disposed in line along the major axis of the formation. Thelaboratory tests carried out in connection with the well arrangement setforth in FIG. 4, wherein all the production wells are disposed in linealong the major axis of the formation, showed that such an elongated,elliptical water drive formation would be produced to the extent of 88.1percent thereof by these '12 wells alone, i.e. 88.1 percent of theformation would be swept. Although the rate at which petroleum isproduced from such a formation is less than the rate of production fromthe same formation by employing a larger number of production wells inthe manner indicated in FIGS. 1 through 3, still the overall recovery ishigh, and higher than that exhibited by the tests carried out withrespect to the well arrangements illustrated in FIGS. 1 and 2, so thatsubstantially less capital expenditure is required to exploit apetroleum-producing formation in accordance with the well arrangement ofFIG. 4.

The problem of optimum well density, or spacing, to deplete a producingfield has many facets. It is only natural that a producer would wish toget the greatest possible volume of oil from his various reservoirs andalso to do it with the least possible number of wells. Assuming thatrecovery is proportional to the area swept out, any curve of recoveryversus the number of wells is influenced by such factors as:

(1) The shape of the field.

(2) Source and type of drive.

(3) Types of production and injection well patterns. (4) Permeabilitydistributions.

(5 Gravitational forces.

(6) Field production practices.

In an investigation concerning these tabulated factors, it is obviousthat an increase in sweepout will not be a linear function of the numberof wells. Somewhere on the slope of any curve showing the plot of thesevariables, there will begin a decrease and probably very sharply. Toinclude an evaluation of the relative effects of all of the factorsmentioned above would require a tremendous amount of time and effort, sothat certain logical starting points and assumptions for a study arerequired. As an example, the shape of a field may be assumed as an idealmodel, to be uniformly thick, nearly flat and elliptical, such type offield occurring in the petroleum producing formations adjacent thePersian Gulf. Further, permeability variations need not be consideredsince their effect would be present for each value of the total numberof wells investigated and would tend to cancel each other.

A study of the sweep-out (R) versus the number of wells (N) in the fieldyielded the data listed in Table I, below, showing the measured valuesof R versus N, together with the number of wells on the axis (n).

Table I Number Percent Wells on Number Percent Wells on of wells svreptaxis of wells swept axis N R n N n l 1 26. 6 1 17 72.0 5 1 2 39. 9 2 1976. 6 7 1 3 51. 5 3 23 77. 3 7 4 12. U 25 79. 6 9 32.6 1 28 83. 3 10 659. 7 4 31 84. 2 11 7 53.1 3 34 86.4 12 8 48. 8 2 40 88. 3 14 9 67.4 546 86. 4 12 10 G2. 4 4 46 90.7 16 1 12 88.1 12 69 95. 4 25 1 No pattern;wells only on axis.

r posed substantially in line along FIG. 5 is a chart of part of thisdata, where it can be seen that there is no definite break in the curve.There is also some scatter, particularly in the lower values of N, wherean increase in N sometimes results in a decrease in R.

FIG. 6 is a plot of R versus 11 which produces a much smoother curvethan that disclosed in FIG. 5 and has no instance of a decrease in R foran increase in it. There appears to be a break in the curve where thevalue of n is aqual to 6 or 7 and a levelling off at about )1 equals 25(and R equals percent). Beyond this value, the curve will still approachpercent as it approaches infinity but the slope is very small.Measurement of the slope of the curve for values of n greater than 25shows that the slope can be less than /2 percent per well, so thatadditional data points would not be reliable enough to Warrant the timerequired for further study.

The data in Table I for R, N and It indicates quite clearly that thesweep-out is not nearly so dependent on N as on 11. Tests which utilizethe same number of axial wells tend to have the same or nearly the samesweep, even though the total number of wells may differ considerably.This is true especially for the higher values of n. The plot in FIG. 6when weighed in conjunction with other factors, helps to determine thebest number of axial wells to use. Sweep-out of approximately 95 percentof the areal extent of the reservoir may be achieved with as few as25-30 wells.

It is recognized that when a field is discovered, a certain number ofdevelopment wells will always be required in order to delineate fieldboundaries and obtain necessary information. It is recognized furtherthat the maximum well potential and the total field productionrequirement will establish a minimum number of wells to be in operation.In other words, the principles described above, when applied to aproducing field will tend to yield the optimum sweep-out of a typicalelongated field.

Although in the practice of this invention, particular emphasis has beenplaced on the exploitation of elongated, substantially elliptical, waterdrive reservoir, the production techniques of this invention are alsoapplicable to so-oalled gas-drive reservoirs and indeed are generallyapplicable to large, elongated reservoirs wherein the ratio (NW) of thelength (l) to the width (w) thereof is greater than 4. The elongatedreservoir applicable in the practice of this invention need not besubstantially elliptical in shape but may be curved, angled erserpentine in configuration, provided the ratio of the overall length tothe overall or average width of the formation (l/w) is at least greaterthan 4.

As will be apparent to those skilled in the art, in the light of theaccompanying disclosure, many changes, alterations and substitutions arepossible in the practice of this invention without departing from thespirit and scope thereof.

I claim:

1. A method of producing petroleum from a uniformly thick, nearly flat,underground petroleum-bearing formation, elongated and substantiallyelliptical in shape with the ratio (a/ b) of the major axis (a) of saidformation to the minor axis (b) thereof being greater than four, whichcomprises penetrating said formation with a plurality of productionwells, and producing petroleum from said formation via said productionwells, the number of said production Wells disposed substantially inline along said major axis of said formation varying from 5 to 30.

2. A method in accordance with claim 1, wherein the production wellsdisposed substantially in line along said major axis are substantiallyequidistant from each other.

3. A method in accordance with claim 1, wherein all the production wellspenetrating said formation are disthe major axis.

References Cited in the file of this patent Jones, Park J.: PetroleumProduction, Oil Production 10 by Water, volume HI, Reinhold PublishingCorporation, 330 West 42d St, N.Y., 1947 (pages 241, 242 relied on).Muscat, Morris: Physical Principles of Oil Production,

first edition, McGraW-Hill Book Co., Inc, N.Y., 1949.

P. 818 relied on.

Uren, L. C.: Petroleum Production Engineering, fourth edition, publishedby MoGraW-Hill Book Co., Inc, N.Y., 1956. (Pp. 50 and 51 relied on.)

1. A METHOD OF PRODUCING PETROLEUM FROM A UNIFORMLY THICK, NEARLY FLAT,UNDERGROUND PETROLEUM-BEARING FORMATION, ELONGATED AND SUBSTANTIALLYELLIPTICAL IN SHAPE WITH THE RATIO (A/B) OF THE MAJOR AXIS (A) OF SAIDFORMATION TO THE MINOR AXIS (B) THEREOF BEING GREATER THAN FOUR, WHICHCOMPRISES PENETRATING SAID FORMATION WITH A PLURALITY OF PRODUCTIONWELLS, AND PRODUCING PETROLEUM FROM SAID FORMATION VIA SAID PRODUCTIONWELLS, THE NUMBER OF SAID PRODUCTION WELLS DISPOSED SUBSTANTIALLY INLINE ALONG SAID MAJOR AXIS OF SAID FORMATION VARYING FROM 5 TO 30.